Field of the Invention
The present invention relates to a printing apparatus, a printing apparatus control method, and a storage medium.
Description of the Related Art
When images are printed on both sides of a sheet, a printing apparatus firstly forms a toner image on a front side of the sheet and fixes the toner image by heat in a fixing unit. In this case, due to the heat form the fixing unit, the sheet is contracted. Then, this image forming apparatus forms a toner image on a back side of the contracted sheet. This causes a displacement of a print position in the main scanning direction and the sub scanning direction on the front side and back side, respectively, of the sheet.
In a printing apparatus described in Japanese Patent Application Laid-Open No. 2003-173109, on a sheet which has a reference position mark at a predetermined position, four measurement position marks which are different from the reference position are printed at predetermined positions. Then, the printing apparatus reads the image of the sheet (hereinafter, referred to as a chart) including the reference position mark and the four measurement position marks, searches all pixels of the generated image data, and detects the position of the reference position mark and the positions of the four measurement position marks. Next, the printing apparatus obtains coordinate of each of the four measurement position marks based on distances between the position of the detected reference position mark and the respective four measurement position marks, and corrects the print position.
To obtain the displacement of the print position, a scaling rate in the main scanning direction, and a scaling rate in the sub scanning direction properly, the position of the reference position mark and the positions of the four measurement position marks in the image data need to be detected correctly.
In the printing apparatus described in Japanese Patent Application Laid-Open No. 2003-173109, it takes time to process the detection of each position of the four measurement position marks in the image data, since it is needed to search all the pixels in the image data generated by scanning the image of the chart.